Continental shelves and deep-sea floors are rich in resources (such as oil, natural gas, methane hydrate, polymetallic nodule, manganese crust, and submarine hydrothermal deposit), and demands for development of marine resources have been increased because of recent steep rise in price of resources. Terrestrial natural resources are unevenly distributed in particular regions, and people should rely on importation from abroad for resources with small domestic production volumes; thus there are not a few geopolitical risks. In Japan surrounded by the seas, in the light of stable supply of resources, ocean areas have been focused as a new frontier for resources development.
As a seabed resources survey technology, such a technology that uses a reflection seismic survey method has already been proposed (see Patent Document 1, and Non-Patent Document 1, for example).
Patent Document 1 describes the following: “generating vibrations (sound waves) near a surface of the sea, in the sea, or at the seabed using a vibration source (wave transmitter), such as an air gun that bursts compressed air into the water, a piezoelectric element, and a super magnetostriction alloy; receiving sound waves reflected and returned from surfaces of the seabed, boundary surfaces of strata under the seabed, or the like on hydrophones (receivers) arranged with intervals on a cable called as a streamer; and performing a survey on boundary surfaces of the strata having different physical properties, which are revealed in the above received records, that is, seismic survey records under the seabed so as to analyze the geological structures”.
Non-Patent Document 1 describes that S-waves (shear waves) have features of being hardly affected by fluids in pore spaces compared to P-waves (compressional waves), and becoming separated after penetrating a stratum where fractures are grown, etc.; and S-waves enable a grasp of structures of oil and gas reservoirs and properties of the reservoirs, which is hard to be attained by using a P-waves seismic reflection survey alone; therefore, the S-wave seismic reflection survey has come under the spotlight.